"Teams will fan out across the Sierra Nevada on Thursday to perform their final snow survey of the season, a closely watched rite of spring that helps determine how much water will flow to farms and cities in coming months.

But 18,000 feet above the Sierra slopes, an airborne experiment is underway that could revolutionize that ritual.

Starting in early April, researchers have made weekly flights over the upper Tuolumne River basin, taking sophisticated instrument readings of the snow depth and reflected sunlight. The information, coupled with data from the ground measurements, promises to paint the most comprehensive snowpack picture that water managers have ever had.

'This is the first time that we've actually known how much water there is,' said Tom Painter, a scientist with NASA's Jet Propulsion Laboratory in La Cañada Flintridge who is overseeing the aerial project with the California Department of Water Resources."